First of all, Welcome!
Now, about those chickies. At only a few weeks of age, all of the chicks regardless of gender will have small "spur bumbs" on their lower legs towards their ankles. Most roosters, as I understand, do not begin developing full on spurs until much older.
Most feed stores only sell pullets, as long as they are not bantam. So the chances are pretty good that you will have mostly hens in there, assuming that your feed store does not order straight run. If you post pics of them* we will be able to help you determine what sex they are.
* In order to post pics on this site, you must first load them onto a host site, such as
www.photobucket.com . Then, click on the "img code" beneath the uploaded image, and paste it into your post. This should get the pic up so we can see it.
Again, welcome!!!